1. Field of the Invention
The invention relates to the field of power cables, and more particularly to a multifunctional tester for measuring the insulating properties of cross-linked polyethylene (XLPE).
2. Description of the Related Art
The physical and chemical performances of cross-linked polyethylene (XLPE) are subject to its crosslinking degrees and operating environments, so that it is necessary to know the electric performance differences of XLPE. At room temperature or a slightly lower temperature, the physical and chemical performance differences of XLPE having different crosslinking degrees may be small, but as a polymer material in a semi-crystalline state, the XLPE has a relatively low melting temperature. In conditions of a relatively high temperature, the physical and chemical performances of XLPE having different crosslinking degrees obviously vary from each other because of the semi-crystalline property of the XLPE. In actual operation of power cable, an operating temperature of the insulating layer may reach between 70 and 90° C., and the operating temperature may reach 105° C. in emergency. Thus, the electric performance of XLPE is required to be tested at different environment temperatures.
Testers for measuring insulating properties of XLPE often employ a needle-plate electrode structure. One electrode of a high voltage terminal employs a needle-like structure having a certain radius of curvature, and the other electrode of a low voltage terminal employs a circular plate structure. Meanwhile, a handheld infrared thermometer is used to measure the temperature of the insulating oil. However, testers of such structures have the following problems:
1. As the needle-plate electrode structure is used, when a test piece is mounted, uneven force may be exerted on the test piece because of manual operation, thereby influencing the strength of the voltage field.
2. The needle-like electrode is easy to be damaged during the test, thereby resulting in variation of the radius of curvature.
3. It is difficult to operate and real-time monitor the variation of the oil temperature when using the handheld infrared thermometer to measure the temperature of the insulating oil. In a word, measuring conditions of the existing tester easily change, which results in inaccurate measuring.